Boost converters are generally employed to provide a stepped up voltage for driving connected loads. Most step-up DC-DC converters adopt asynchronous switches like diode or schottky diode as a switch because they don't need a driving circuit unlike other synchronous switches like BJT, MOSFET, IGBT, and the like. The configuration of an asynchronous DC-DC boost converter does not permit a cut-off of the power path from the input power supply to the output load. If the input power supply voltage is higher than the output voltage during a normal operation, a short circuit is envisaged and a huge current may flow from the input to the output through and inductor and an asynchronous switch comprising the DC-DC boost converter circuit. If the power path is not cut off, the high short current can burn out the inductor or the asynchronous switch. Therefore, a short circuit detection method is necessary and the short circuit signal should be conveyed to the input power supply controller or an isolation switch driver to cut off the power path.
An asynchronous DC-DC boost converter comprises a controller to control the functioning of circuit components besides detecting a short circuit condition and protecting circuit components from high short circuit current. The protection controller typically comprises a comparator that compares a sensing voltage generated by the current through the asynchronous DC-DC boost converter with a short circuit detection threshold voltage reference. The comparator compares both the voltage signals and accordingly provides a signal to a disabling means that is used to cut off the supply of input power to the load. This conventional converter includes a current sensing circuit typically comprising resistors and capacitors in a predetermined configuration for determining the current flowing through the load. Whenever, there is a short in the asynchronous DC-DC boost converter or in the load circuit, high current flows to the system ground through a predefined resistor and correspondingly a dropout voltage is generated. The dropout voltage is then provided as an input to the comparator for comparing with short circuit detection threshold voltage reference and accordingly the input power supply is disconnected from the asynchronous DC-DC boost converter. The controller thus ensures that the input power supply is cut off in the event of a short circuit.
The operation of the aforementioned controller is based on the short circuit current that is transferred to an input of the comparator. The short circuit resistor used for current sensing requires an additional filter circuit in parallel to remove undesired noise in the circuit. The short circuit resistor needs to have an optimum value to ensure accuracy and at the same time be enough to avoid high power loss, thus increasing the cost of controller circuit. The short circuit resistor needs to be precisely calibrated for sensing the short circuit current which makes its usage in the circuit expensive. Also, the power loss due to short circuit resistor cannot be neglected as it always consumes power during normal operation of the converter.
Therefore, there is a need for a better and efficient protection controller for asynchronous DC-DC boost converters which can precisely detect high short circuit current and protect the asynchronous DC-DC boost converters and the load from burn out.